The video below focuses on a new capability in Hyper-V R2 RC (download) called “Dynamic Storage,” which allows an administrator to add or remove a virtual hard disk (VHD) or pass through disk, to a running virtual machine, without incurring any downtime for that virtual machine.  This is particularly useful, when, for example, you want to backup a virtualised SBS 2008 Server, using the in-guest SBS backup tool as the disk you add to the VM, can in fact be a raw, pass-through USB disk, attached to the host box.

Source:→ virtualboy